The invention relates to a dryer with a drying chamber for items to be dried, which features a process air guide for guiding process air through the drying chamber as well as a heat pump with a heat sink which is arranged in the process air duct and through which the process air can flow in an outlet air direction and a heat source arranged in the process air guide and through which the process air can flow in an inlet air direction for heating the process air. Such a vented dryer is based on the abstract to be found in the database “Patent Abstracts of Japan” relating to publication JP 2004 089415 A.
Dryers for items of washing and similar objects are usually embodied as vented dryers or condenser dryers. With vented dryers a stream of air is sucked in from the surroundings of the dryer, heated up, passed over the objects to be dried and subsequently discharged from the dryer as “vented air.” This vented air contains the moisture to be extracted from the objects to be dried and can therefore not simply be expelled into a building since the moisture would condense therein; instead the air must be vented from the building using an appropriate vent hose. This is a constructional disadvantage of the vented air dryer, which in other respects is very simple in its construction and can be marketed at low cost. A condenser dryer, the functioning of which is based on removing the condensation from the objects to be dried by means of process air guided in a closed circuit, does not need any vent hose for removing the moisture-laden process air since the moisture condensed within it is stored as liquid and disposed of after the drying has ended and it can therefore be used in an internal bathroom or an internal kitchen of a larger living space. All this applies both to tumble dryers designed specifically for drying washing and to so-called washer-dryers which can both wash and dry washing. Any subsequent reference to a dryer thus applies both to an appliance for drying and also to an appliance intended for washing and drying.
In a vented air dryer, after the moisture-laden air passes through a laundry drum, it is vented from the dryer without any heat recovery generally being undertaken. A vented air dryer with heat recovery is known from the abstract cited above and document DE 30 00 865 A1 respectively. With a vented air dryer with heat recovery, surrounding air (of e.g. 20° C. and 60% relative humidity; so-called inlet air) flows into an air-air heat exchanger or a heat pump and is heated up there as the hot air coming from the drying chamber cools down. In the heat exchanger (e.g. air-air heat exchanger) the moist process air is cooled down, so that water contained in the moist process air condenses. Depending on the cooling power or the exchange of heat, condensation occurs which is collected or pumped into a container (condensation tray) for later disposal.
Both in a conventional vented air dryer and also in a conventional condensing dryer the heat supplied to the process air is largely lost. In a vented air dryer the heat is discharged with the process air laden with moisture from the objects to be dried, in a condenser dryer the heat passes via a heat exchanger into a cooling medium, usually cool air from the surroundings of the dryer, and is thus likewise lost.
DE 40 23 000 C2 describes a tumble dryer with a heat pump in which an inlet air guide is arranged in the process air duct between the condenser and the evaporator which can be closed off with a controllable closure device.
DE 197 38 735 C2 describes a condensing dryer with a closed drying air circuit which is equipped with a heat pump. The heat pump is embodied as a device operating on the absorber principle of which the absorber forms a third heat exchanger, through the primary circuit of which a coolant flows and via the secondary circuit of which the drying air flowing out of the second heat exchanger is fed back into the secondary circuit of the first heat exchanger.
In addition DE 43 06 217 B4 describes a program-controlled tumble dryer, in which the process air is directed by means of a fan in a closed process air duct, in which closure devices arranged in a specific manner are located. Depending on the operating state (heating-up phase, tumble drying phase, reaching the maximum permitted temperature) the closure devices are actuated in a suitable manner.
With a condenser dryer equipped with a heat pump the cooling down of the heated moisture-laden process air and the condensing out of the moisture contained therein essentially occurs in a subsequent first heat exchanger of the heat pump known as a “heat sink”, especially an evaporator, where the transmitted heat is used for vaporization of a coolant circulating in the heat pump. Such coolant, evaporated as a result of the heating up, is fed via a compressor, a second heat exchanger of the heat pump which will be referred to below as the “heat source” and in this case is a condenser for the coolant, where, as a result of the condensation of the gaseous coolant heat is released, which is used in its turn for heating up the process air before it enters the drum. The vaporized coolant passes through a throttle which reduces its pressure and returns to the evaporator, in order to evaporate there while once again accepting heat from the process air.